OK this is good.
For the sleeves, the 28.5cm mark is showing you where to place the top of the sleeve.You can fold the sleeve in half lengthwise and pin the halfway point of the sleeve top to the shoulder seam. The corner of the sleeve top (where the top of sleeve meets the side edge of the sleeve) should be pinned to the 28.5cm mark on each side. Pin the right sides together and line up the seam between the sweater body and the sleeve along the length from one 28.5 mark to the other with the shoulder pin at the halfway point.